In known seats of this type, the sleeve over the seat back completely covers the casing front face of the safety device, this sleeve being provided with a tearable seam corresponding said front face.
These known seats have the following drawbacks:
it may be difficult to accurately position the tearable seam of the sleeve in relation to the casing front face, since the sleeve completely covers the casing; if this positioning is badly done the safety device may malfunction or even not function at all in the event of the vehicle being involved in an accident, PA1 it is necessary to validate the correct operation of the safety device for each model of sleeve liable to cover the seat back, since the operation of said safety device requires the tearing of said sleeve: considering the great number of possible sleeve models for each vehicle model, this involves very numerous and expensive tests. PA1 the groove which surrounds the casing front face is secured to said casing; PA1 the groove which surrounds the casing front face is formed in a single piece with said casing; PA1 the groove which surrounds the casing front face has approximately a U shaped section, with an external side wall, an internal side wall and a bottom which connects said external and internal side walls, the internal side wall belonging to the casing; PA1 the groove which surrounds the casing front face has approximately a U shaped section, with an external side wall, an internal side wall and a bottom which connects said external and internal side walls, the external side wall comprising inwardly projecting flanges which constitute said additional means of retention, the means of retention secured to the edge of the sleeve being constituted by an approximately J shaped flexible section which is open outwards from the seat back and which has, on the one hand, an internal branch fixed to the edge of the sleeve and, on the other hand, an external branch which hooks itself behind the projecting flanges of the external side wall of the groove.